1. Field of the Invention
The present invention relates to a driving method of a liquid discharge head using an actuator as a source for generating liquid discharge energy, and a liquid discharge apparatus including the liquid discharge head using the actuator as the source for generating liquid discharge energy. The present invention can be applied to a printing apparatus for printing text or images on paper, fabric, leather, or nonwoven fabric, and a patterning apparatus or coating apparatus for applying liquid to a substrate, plate material, solid object or the like.
2. Description of the Related Art
Various proposals have been made for a liquid discharge head mounted in a liquid discharge apparatus which can be represented by an ink jet recording apparatus. Particularly, a liquid discharge head using an actuator as a source for generating liquid discharge energy has a merit in that any type of liquid (ink) is suitable for discharge.
Recently, in order to reduce deformation (curling or cockling) of a recording medium due to water contained in ink that is discharged from the liquid discharge head, use of high-viscosity ink with a reduced amount of water in the ink has been considered.
On the other hand, the method of using a piezo head which is a representative example of the actuator used as source for generating liquid discharge energy include “pull-shot” and “push-shot”. The former is a discharge method of expanding individual liquid chambers and then contracting them and the latter is a discharge method of contracting the individual liquid chambers and then expanding them.
In the case of discharge of the high-viscosity ink, in terms of a reduction in loss of discharge energy, the “push-shot” is desirable.
A technique is disclosed in Japanese Patent Application Laid-Open No. 2008-155537 for enhancing a refilling ability by providing a second piezoelectric element while employing the push-shot method and simultaneously enhancing discharge efficiency thereby enabling high-frequency discharge of high-viscosity ink.
In addition, a technique is disclosed in Japanese Patent Application Laid-Open No. 2001-253071 for reducing a time to refilling ink by providing a second piezoelectric element while employing the push-shot method.
However, when the description of Japanese Patent Application Laid-Open No. 2008-155537 is examined thoroughly, there are many unclear points on whether the refilling ability is enhanced. That is, in the technique disclosed in Japanese Patent Application Laid-Open No. 2008-155537, first, a voltage applied to a first piezoelectric element is increased to contract the individual liquid chambers to discharge liquid droplets. Thereafter, the voltage applied to the first piezoelectric element is returned to its initial value to expand the contracted individual liquid chambers and thus refilling the liquid chambers with ink (drawing in ink) from a common liquid chamber. However, during the refilling with ink from the common liquid chamber, a meniscus in a discharge port is pulled back in the direction of the common liquid chamber. Moreover, in Japanese Patent Application Laid-Open No. 2008-155537, with the start of the operation for expanding the individual liquid chambers, a cross-section of a flow path is expanded by reducing a voltage applied to the second piezoelectric element, so as to enhance refilling efficiency of the ink from the common liquid chamber (drawing of ink).
However, right after this, the voltage applied to the second piezoelectric element is returned to its initial value so as to contract the expanded cross-section of the flow path. In regard to this, in Japanese Patent Application Laid-Open No. 2008-155537, it is described that ink is pushed into the individual liquid chambers by contracting the cross-section of the flow path and thus it is efficient.
On the examination by the inventors, since the second piezoelectric element is provided at a position close to the common liquid chamber with a small flow resistance, most of the ink is pushed back in the direction of the common liquid chamber rather than to the individual liquid chambers by the operation of contracting the cross-section of the flow path. Accordingly, it is thought that the increase in efficiency of the refilling ability of the individual liquid chambers cannot be expected.
In addition, in the technique disclosed in Japanese Patent Application Laid-Open No. 2008-155537, it is unclear whether the meniscus can be promptly returned to its initial position in the discharge port. If the meniscus is not promptly returned, speedup of drive frequency cannot be realized.
Next, when the description of Japanese Patent Application Laid-Open No. 2001-253071 is examined thoroughly, there are many unclear points on whether the refilling time is reduced. That is, in the technique disclosed in Japanese Patent Application Laid-Open No. 2001-253071, the voltage applied to the second piezoelectric element close to the common liquid chamber is increased in advance to contract the cross-section of the flow path. Subsequently, the voltage applied to the first piezoelectric element is increased to contract the individual liquid chambers and discharge liquid droplets, and then the voltage applied to the second piezoelectric element is returned to its initial value so the cross-section of the contracted flow path is expanded and ink is refilled (ink is drawn in) from the common liquid chamber. In addition, after the operation for expanding the cross-section of the flow path, the voltage applied to the first piezoelectric element is returned to its initial value to expand the contracted individual liquid chambers. In Japanese Patent Application Laid-Open No. 2001-253071, the refilling flow by the second piezoelectric element is added to the refilling flow by the first piezoelectric element by the above-described operation, and thus the efficiency of the refilling ability (drawing of ink) is raised.
However, in the final operation of allowing expansion by the first piezoelectric element, there is a flow which returns the meniscus to the side of the common liquid chamber during the returning process in the discharge direction. As a result, it is thought that the increase in efficiency of the refilling ability of the individual liquid chambers cannot be expected.
In addition, it is unclear whether the meniscus can be promptly returned to its initial position in the discharge port. If the meniscus is not promptly returned, speedup of drive frequency cannot be realized.